Many human enzymes serve as targets for the action of pharmaceutically active compounds. Several classes of human enzymes that serve as such targets include helicase, steroid esterase and sulfatase, convertase, synthase, dehydrogenase, monoxygenase, transferase, kinase, glutanase, decarboxylase, isomerase and reductase. It is therefore important in developing new pharmaceutical compounds to identify target enzyme proteins that can be put into high-throughput screening formats. The present invention advances the state of the art by providing novel human drug target enzymes related to the steroid oxidoreductase subfamily.
The present invention has substantial similarity to 3.beta.-hydroxy-5-C27-steroid oxidoreductase (C.sub.27 3.beta.-HSD). 3.beta.-hydroxy-5-C27-steroid oxidoreductase involves in the synthesis of bile acids.
Bile acids are important components of normal physiology with essential functions in the liver and small intestine. Their synthesis in the liver provides a metabolic pathway for the catabolism of cholesterol and their detergent properties promote the solubilization of essential nutrients and vitamins in the small intestine. The synthesis of bile acids was thought to involve as many as three separate pathways. Each pathway differs in the initial steps and in the involvement of distinct sterol 7-hydroxylase enzymes that add an essential hydroxyl group to carbon seven of the sterol ring. After the addition of this group, the next step in each pathway is catalyzed by a 3.beta.-hydroxy-5-C27-steroid oxidoreductase, which isomerizes the 5 bond to the 4 position and oxidizes the 3.beta.-hydroxyl group to a 3-oxo moiety on intermediates with 27 carbon atoms.
The 3.beta.-HSD enzyme family consists of a large number of proteins that are present in both prokaryotes and eukaryotes. They are proposed to play a wide variety of anabolic and catabolic roles in intermediary metabolism, and, consistent with this broad function, they are expressed in abundance in organisms ranging from viruses to humans.
C.sub.27 3.beta.-HSD enzyme deficiency is marked by accumulation of C.sub.27 sterol intermediates of bile acid synthesis, progressive intrahepatic cholestasis, and no endocrine abnormalities. Inherited conditions that prevent the synthesis of bile acids can cause the accumulation of cholesterol and liver dysfunction (cholestasis), underscoring the essential role of bile acids in metabolism. Progressive neonatal intrahepatic cholestasis is marked by jaundice, fat-soluble vitamin deficiency, and lipid malabsorption and is a rare condition of diverse etiologies. Among the causes of this disorder are inborn errors of metabolism that affect the production and secretion of bile. In the absence of a normal bile flow and bile acid pool size, the end products of heme metabolism are not secreted, and their accumulation causes the characteristic jaundice. Dietary fat-soluble vitamins are not effectively taken up in the intestine, leading to deficiencies in hemostasis, and hydrophobic lipids such as long-chain fatty acids and cholesterol are poorly absorbed causing fatty stools. It has been reported that a deficiency of this enzyme can be treated by oral administration of bile acids. For a review relate to the oxidoreductase, see Schwarz et al., J Clin Invest 2000 Nov; 106(9):1175-84.
Enzyme proteins, particularly members of the steroid oxidoreductase subfamily, are a major target for drug action and development. Accordingly, it is valuable to the field of pharmaceutical development to identify and characterize previously unknown members of this subfamily of enzyme proteins. The present invention advances the state of the art by providing previously unidentified human enzyme proteins, and the polynucleotides encoding them, that have homology to members of the steroid oxidoreductase subfamily. These novel compositions are useful in the diagnosis, prevention and treatment of biological processes associated with human diseases.